Speaker
Pelin Kurt
Description
We present early results of the CMS experiment from PbPb collisions at $srqrt{s_{NN}}$ = 2.76 TeV, probing quark and gluon matter at unprecedented values of energy density. The capabilities of the CMS apparatus allows us to investigate various hard probes, as well as bulk particle production and collective phenomena, using the calorimetry, muon and tracking systems covering a large range in pseudorapidity, complemented by a flexible two-level trigger system. One of the most important early observations was that dijets at high pT are found to be increasingly unbalanced as a function of collision centrality. The angular distribution of jet fragments has been also studied in these events indicating a softening and widening of the subleading jet fragmentation pattern. The overall pT-imbalance can be recovered by including tracks found at low pT and at large angles with respect to the jet axis. Furthermore, the pT-distribution of charged tracks (jet fragments) has been measured using various jet triggers, extending to pT=200 GeV/c in pp collisions at 7 TeV, and a reference spectrum is constructed to compare to PbPb collisions at 2.76 TeV/nucleon pair. The inclusive production of isolated prompt photons has also been studied in pp collision. The corresponding ongoing efforts for PbPb collisions will be reviewed. CMS is also well equipped to measure muons and dimuons in the high multiplicity environment of heavy ion collisions. Inclusive and differential measurements of the Z boson yield show no sign of modification with respect to NLO pQCD calculations. Dimuon decays of the J/psi particle and the Upsilon family are also investigated and results will be presented for pp as well as for PbPb collisions. Two-particle correlations in both collision systems will be presented at various LHC beam energies, and the complex two-dimensional structure with various short and long range correlation features in pseudorapidity will be discussed, including the long range, same-side ridge in high multiplicity pp and central PbPb events. Azimuthal angle correlations of charged hadrons were also measured as a function of transverse momentum, centrality and pseudorapidity, using the event-plane, cumulant and Lee-Yang zeros methods, featuring different sensitivities to non-flow correlations. An outlook to odd Fourier-components of the azimuthal angle distributions will also be presented. Finally, the transverse energy produced by the heavy ion collision as a function of centrality will be discussed as well, in a wide range of pseudorapidity, to help disentangle the interplay of initial state end final state effects on energy flow, and to study the baryon energy loss and the subsequent development of the pressure of the hot partonic system.
